The present invention relates generally to interlocking arrangements for panels, and more particularly to a locking arrangement for panels wherein a locking tab forms a cooperative slide locking engagement with a pair of locking slits.
In the packaging of articles, and particularly of one or more articles in wrap-around type cartons, locking arrangements are frequently used for maintaining closure of the carton about the articles. It can be appreciated that such locking arrangements must be securely and reliably engaged, and must remain in such condition until the carton is opened.
One well-known form of locking arrangement comprises a locking tab and cooperating slit. An example of this type of locking arrangement can be seen in U.S. Pat. No. 3,249,284 (Wood). In this example, as is typical, the locking tab includes a head portion attached along a relatively narrow neck to a panel of the carton. The tab includes at least one shoulder, i.e., that portion of the tab where the head connects with the relatively narrow neck. On an opposite panel of the carton, a slit is formed into which the tab may be inserted. Following insertion, the tab shoulder engages the end of the slit, preventing the tab from being withdrawn, and thereby securing the lock.
For locks of this type, it is advantageous to provide means to facilitate opening of the slit for receiving the locking tab as it is inserted. Otherwise, the tab or slit may be damaged during engagement, or the tab may miss engagement with the slit altogether. Thus, it is known to arrange the slit such that as a leading portion of the panel in which the slit is formed is folded away, the slit is opened. Such an arrangement may be seen, for example in U.S. Pat. No. 4,600,140, in which the slit includes angled portions for creating the opening. However, it is also important to ensure that once inserted, the tab remains firmly engaged with the slit. When the leading edge panel has been folded away, the edge panel may not completely return to its original position, thereby leaving the slit partially opened.
One way in which secure retention can be accomplished is to have a portion of the tab which is folded over into overlapping relation with the main tab body. After insertion, the folded portion is released and at least partially unfolds, thereby providing additional security to the lock. An example of this approach can be seen in the above-referenced U.S. Pat. No. 4,600,140. One disadvantage of this approach, however, is the additional complexity required in machinery for forming and locking cartons.